In heat assisted magnetic recording, information bits are recorded on a data storage medium at elevated temperatures, and the data bit dimension can be determined by the dimensions of the heated area in the storage medium or the dimensions of an area of the storage medium that is subjected to a magnetic field. In one approach, a beam of light is condensed to a small optical spot onto the storage medium to heat a portion of the medium and reduce the magnetic coercivity of the heated portion. Data is then written to the reduced coercivity region.
One example of a recording head for use in heat assisted magnetic recording generally includes a write pole and a return pole magnetically coupled to each other through a yoke or pedestal, and a waveguide for focusing light onto the storage medium. The waveguide is positioned between the write pole and the return pole. Light from a laser is coupled into the waveguide and transmitted through the waveguide to produce a tightly focused laser spot on the storage media. The power in this spot determines the width of the recorded track and the quality of the recorded transitions.
It would be desirable to have a method to measure or monitor this power once the head is assembled in a drive.